Paper No. 20-7
Presentation Time: 1:30 PM-5:30 PM
COMPARATIVE PALEO-LIMNOLOGY OF RAFTING PROCESSES IN LATE TRIASSIC LACUSTRINE RECORDS
CHANG, Clara1, KINNEY, Sean T.1, FANG, Yanan2, CHO, Sun A.3, LEE, Madison3, SHA, Jingeng4 and OLSEN, Paul E.1, (1)Department of Earth and Environmental Sciences, Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964-1000, (2)CAS Key Laboratory of Economic Stratigraphy and Palaeogeography, Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and Paleoenvironment, Nanjing, 210008, China; Department of Earth and Environmental Sciences, Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964-1000, (3)Cresskill High School, 1 Lincoln Drive, Cresskill, NJ 07626, (4)CAS Key Laboratory of Economic Stratigraphy and Palaeogeography, Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and Paleoenvironment, Nanjing, 210008, China
Atmospheric carbon dioxide during the late Triassic was extremely high (~1000-6000 ppm) (1) and the period has been characterized as one of the few times in Earth’s history lacking polar glacial ice. Recently, however, Olsen et al. (2) argued that seasonal freezing occurred in the paleo-arctic (~70°N) Late Triassic age lacustrine deposits in the Junggar Basin, China (3). One major observation is anomalously large (0.1-12 mm) “floating” lithic clasts interpreted to be lake ice rafted debris in otherwise suspension-dominated mudstones associated with fish and amphibian fragments. This discovery provides an entirely new context with which to interpret early dinosaur evolution and consequences of the End-Triassic Extinction (ETE) (4).
Studies on ancient ice rafting are often criticized because the clasts can be confused with the products of algal and root rafting. Here, we use quantitative granulometry to distinguish the different processes. We present unique grain size distributions and microfacies descriptions of paleo-arctic ice-rafted Junggar Basin samples as well as broadly contemporaneous paleo-tropical rift-lake algal-rafted sediments from rift basins of eastern North America. We present new methods on mudstone disaggregation and modified analytical procedures for quantitative granulometry on these sedimentary rocks.
Specific, quantitative criteria to distinguish kinds of lithic clast rafting are necessary as we continue to explore deep-time lacustrine environmental archives for evidence of freezing conditions. Quantitative criteria will be broadly useful in paleoclimate reconstructions using both lithified and modern lacustrine sediments and will allow more rigorous climate reconstructions.
References:
1, Schaller MF et al. (2015) GSA Bulletin 127(5-6):661-671.
2, Olsen PE et al. (2018) Geophysical Research Abstracts 20:EGU2018-11440-2.
4, Sha J et al. (2015) PNAS 112(12):3624-3629.
3, Olsen PE et al. (2018) GSA Abst Prog 50(6) doi: 10.1130/abs/2018AM-325061
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